Collision avoidance is a basic requirement of all drivers of ground vehicles, such as automobiles, trucks, motorcycles (hereinafter referred to as “vehicles”) while driving to a desired destination. As shown in FIG. 1, the basic collision avoidance maneuvers of a given vehicle A (hereinafter referred to as the “driven vehicle”), in order to avoid a collision with an obstacle O, e.g. a stalled vehicle, in its forward path, include a stopping maneuver S in its current lane and a lane change maneuver L by which driven vehicle A safely merges with vehicles B and C in the neighboring lane.
Various factors such as the mechanical capabilities of the driven car, passenger comfort, and the trajectories (paths and velocity profiles) of moving vehicles in neighboring lanes are taken into account while planning and executing a safe collision avoidance maneuver. At times, a collision is unavoidable due to the need to consider such a large number of factors, often at a split second, while hindered for example by poor visibility, high speed, fatigue, and old age.
In order to increase the rate of safe collision avoidance maneuvers, the prior art has introduced computer generated avoidance maneuvers for completely automated vehicles or for humanly driven vehicles.
U.S. Pat. No. 5,343,206 discloses a method for avoiding a collision between a motor vehicle and obstacles in the path of the vehicle by forming a radar map of the area in front of the vehicle, reconstructing the geometry of the road, identifying its edges, detecting the position and speed of the vehicle with respect to the road, determining the presumed path of the vehicle on the basis of the road geometry and the maneuver being carried out by the vehicle at that instant, detecting objects on the radar map found lying in the presumed path of the motor vehicle and displaying the map found in a perspective representation, ignoring objects which are off the road and indicating objects in the path of the vehicle in a different manner according to their hazard and if appropriate, generating alarms of an acoustic type.
EP 1223093 discloses a braking control system that includes a control unit which is electronically connected to an object detector and a host vehicle speed sensor for automatically controlling, depending on a host vehicle speed and a relative distance, a braking force needed for an automatic braking operation. When the host vehicle is approaching an object ahead, such as a preceding vehicle, the control unit detects the presence or absence of a driver's intention for lane-changing. In the presence of the driver's intention for lane-changing, the control unit inhibits preliminary braking control, initiated prior to the driver's braking action, or reduces the degree of limitation on supplementary braking control, through which a value of a controlled quantity is brought closer to a target deceleration rate needed for collision-avoidance.
U.S. Pat. No. 5,529,138 discloses an automobile collision avoidance system based on laser radars for aiding in avoidance of automobile collisions. The system detects the location, the direction of movement, the speed and the size of all obstacles specifically and precisely. A steering wheel rotation sensor or a laser gyroscope is utilized to give information of system-equipped vehicle's directional change. The system compares the predicted collision time with the minimal allowable time to determine the imminency of a collision, and when determined, provides a warning. An optional automatic braking device is used when the vehicle user fails to respond to a warning. Furthermore, a wheel skidding detecting system based on a discrepancy between the directional change rate predicted by a steering wheel rotation sensor and the actual directional change rate detected by a laser gyroscope is also disclosed.
U.S. Pat. No. 5,870,303 discloses a method for controlling the maneuvers of a robotic vehicle in the presence of obstacles by using a three-dimensional configuration space which propagates cost waves in configuration space and using budding search strategy.
Obstacle avoidance by automated vehicles that merge with neighboring traffic has been achieved by first producing a gap in a neighboring lane and then executing a lane change maneuver into the produced gap [Godbole et al, “Design of Emergency Maneuvers for Automated Highway System: Obstacle Avoidance Problem,” CDC 1997]. The drawback of such an approach is that the driven vehicle is dependent upon the maneuvers of neighboring vehicles with which the driven car communicates and which may not accurately perform the maneuver requested by the driven vehicle.
In another approach, the minimum clearing distance, beyond which an obstacle cannot be avoided at a given initial speed, is determined. [Shiller et al, ASME Journal of Dynamic Systems, Measurement and Control, Vol. 120, No. 1. March 1998, pp. 37-44]. Although a lane change maneuver is generally the most desirable option since traffic flow is least disturbed, such a maneuver may not be immediately feasible, depending on the distance to the obstacle, speed of the driven vehicle, and the volume of traffic in the neighboring lanes. If a lane change maneuver is not feasible, a full stop is generally the best alternative. However, if the initial speed and distance from the obstacle are insufficient for a full stop, the driven vehicle needs to decelerate until the traffic conditions allow a lane change maneuver to take place. Once the driven vehicle approaches the obstacle within the minimum clearing distance, a collision is unavoidable.
Determination of the minimum clearing distance CD is illustrated in FIG. 2. The minimum clearing distance is the longitudinal distance along the X-axis, which represents the initial direction of driven vehicle A, from initial position xo of driven vehicle A until intersection point 10, at which a vertex of driven vehicle A intersects a vertex of the stationary obstacle O as driven vehicle A follows an optimal lane transition maneuver until final position Xf. An optimal lane transition maneuver is a maneuver that minimizes longitudinal displacement of driven vehicle A without collision while taking into account the initial speed {dot over (χ)}o, vehicle dynamics, and road conditions. Similarly, an optimal lane transition maneuver may be carried out for a moving obstacle, as well.
FIG. 3 graphically illustrates three regimes of vehicular driving conditions in terms of the difficulty in avoiding a collision with a detected obstacle. Each regime is representative of various combinations of vehicular speed and minimum clearing distance from the obstacle (hereinafter referred to as “states”). The clearance curve is representative of the relationship between initial speed {dot over (χ)}o and minimum clearance distance CD for an optimal lane transition maneuver, which may be generated while considering the driver's reaction time, as well as the motion of the obstacle. The clearance curve delimits the boundary of safe states of a driven vehicle (Region II), which result in avoidance of the obstacle, from states which result in an unavoidable collision (Region III). The stopping distance curve delimiting the boundary of various states of a driven vehicle which facilitate deceleration thereof to a full stop without colliding with the obstacle (Region I) is also illustrated. When the obstacle is detected in Region I, sufficient time remains for a full stop or a lane change maneuver without changing speed. When the obstacle is detected in Region II, e.g. at point 11, the driven vehicle is precluded from making a full stop, and must perform a lane change maneuver. The driven vehicle may decelerate, e.g. from point 11 to point 13, and then perform an optimal lane transition maneuver, after which the state of the driven vehicle corresponds to the clearance curve. When the obstacle is detected in Region III, e.g. point 15, the driven vehicle is precluded from performing a lane change maneuver, and is recommended to remain in the current lane and to decelerate at the maximum deceleration. By being decelerated to a maximum level, the driven vehicle avoids a more dangerous collision and is involved in a head-on collision at a lower speed, e.g. at point 17, at which speed the driven vehicle is generally designed to withstand the resulting impact such as by means of a bumper. If the driven car were to perform a lane change maneuver in Region III, a more dangerous off-center collision or loss of control is liable to result.
Although such an approach is effective in terms of determining a suitable avoidance maneuver with a detected stationary (or moving) obstacle, this approach does not directly consider the vehicles in the neighboring lane nor when vehicles move in an unpredicted fashion. Such situation may be handled using a method for collision avoidance of moving obstacles, by P. Fiorini et al, International Journal of Robotics Research, 17(7): 760-772, July, 1998, which is based on the concept of velocity obstacles (VO). As referred to herein, a velocity obstacle is a set of absolute velocity vectors of a driven vehicle that result, at a future time, in a collision with a given moving obstacle.
Referring now to FIG. 4, the initial position of a driven vehicle and a moving obstacle are indicated by points A and B, respectively, while circle B represents the obstacle. The initial velocity vectors of driven vehicle A and moving obstacle B are generated and are indicated by VA and VB, respectively. The relative velocity vector between A and B is indicated by VAB. A planar sector (hereinafter referred to as a “collision cone”), which is representative of all possible relative velocity vectors VAB and having an apex coinciding with A, is then generated. Collision cone 20 is bounded by lines R and F which originate at A and are tangent to circle B. Therefore any relative velocity vector VAB coinciding with collision cone 20 will result in a collision and any relative velocity vector VAB not coinciding with collision cone 20 will result in collision-free motion, assuming that obstacle B maintains its current shape and speed.
In order to determine an optimal collision avoidance maneuver with respect to a plurality of obstacles, it is graphically advantageous to translate the generated collision cone to point A′, as shown in FIG. 5. By adding velocity vector VB to each velocity vector included within collision cone 20 (FIG. 4), velocity obstacle (VO) 25 is produced, which is representative of all possible absolute velocity vectors VA having an apex coinciding with A′ at the end of vector VB. Since the illustrated VA penetrates VO 25, such an absolute velocity will result in a collision. Similarly, a plurality of velocity obstacles, e.g. VO 25 and 26, for a corresponding number of obstacles, e.g. B and B1, may be generated, as shown in FIG. 6. Any absolute velocity vector VA that is outside of all of the velocity objects, such as the absolute velocity vector VA illustrated in FIG. 6 the end of which coincides with border R′ of VO 25 at point 29, will result in collision-free motion, assuming that the obstacles maintain their current shape and speed. Therefore, any velocities of driven vehicle A that may be represented by a vector that elongates starting at point A and terminates inside the overlapping region between VOs 25 and 26, will result in a collision with obstacle B or B1.
At times, the penetration of an absolute velocity vector into a VO is representative of a collision that is of a negligible risk. Such a predicted collision may occur, for example, after a long time period, if driven vehicle A and the obstacle maintain their current velocity vector. To save valuable calculation time, a VO may be truncated at a predetermined time horizon TH, or time prior to occurrence of a potential collision. As shown in FIG. 7, VO 25 is truncated at predetermined TH such that truncated portion 28 is made to be non-displayable. As the remaining portion of VO 25 is shown to be not penetrated by absolute velocity vector VA, this velocity of A therefore, no longer presents a reasonable risk of collision with obstacle B, within th.
Although the aforementioned prior art methods may provide information regarding the likelihood of a collision, the prior art methods are incapable of determining in real time the most preferred maneuver among a plurality of possible collision avoidance maneuvers. Also, the prior art methods determine a single collision avoidance maneuver for given velocity vectors of a driven vehicle and obstacle, respectively. However, the velocity vectors of the driven vehicle and obstacle are frequently varied in an unpredictable fashion such that the single generated collision avoidance maneuver ceases to be a feasible possibility for preventing a collision. Furthermore, the prior art methods are incapable of determining an optimal collision mitigating maneuver once it is apparent that a collision with the driven vehicle is unavoidable.
It is an object of the present invention to provide a method and system for determining a driver initiated optimal collision mitigating maneuver once it is apparent that a collision with a driven vehicle is unavoidable.
It is an object of the present invention to provide a driver of a vehicle with a set of warnings having escalating severity levels which are associated with vehicular maneuvers, regarding the risk of a collision with stationary and/or moving obstacles in the vicinity of the driven vehicle.
It is another object of the present invention to offer a driver of a vehicle a set of feasible options for avoiding a collision with stationary and/or moving obstacles in the vicinity of the driven vehicle.
It is yet another object of the present invention to determine the most optimal collision avoidance or collision mitigating maneuver in iterative fashion with respect to the instantaneous position and velocity vector of a driven vehicle and detected obstacle.
Other objects and advantages of the invention will become apparent as the description proceeds.